The present invention relates generally to expandable endoprosthesis devices, generally called stents, which are adapted to be implanted into a patient""s body lumen, such as a blood vessel, to maintain the patency thereof, and more particularly to vascular stents that are formed with flow channels to accelerate blood flow therethrough and minimize clot and thrombus formation.
Stents are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means, to help improve the results of the procedure and reduce the possibility of restenosis. Stents also can be used to provide primary compression to a stenosis in cases in which no initial PTCA or PTA procedure is performed. While stents are most often used in the procedures mentioned above, they also can be implanted in another body lumen such as the urethra, esophagus and bile duct.
In typical PTCA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the aorta. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guidewire sliding within the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient""s vasculature and is advanced across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressure to displace the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. Stents are generally cylindrically shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as coronary artery. Stents are usually delivered in a compressed condition to the target location and then are deployed into an expanded condition to support the vessel and help maintain it in an open position. The stent is usually crimped tightly onto a delivery catheter and transported in its delivery diameter through the patient""s vasculature. The stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of the delivery catheter, which expands the compressed stent to a larger diameter to be left in place within the artery at the target location. The stent also may be of the self-expanding type formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen.
At present, there are numerous commercial stents being marketed throughout the world. The use of stents has so far been plagued by certain common problems, including the formation of thrombi and blood clots, and the occurrence of restenosis. Thrombosis is a phenomenon whereby a fibrous clot forms within small cracks and other irregularities in an object, such as may be found on the surface of a stent. Furthermore, turbulence in the blood flow caused by abrupt edges on the stent can also produce stagnant pools of blood, thereby encouraging the deposition of plaque and other materials and the formation of blood clots. In addition, blood flow turbulence is suspected to play in role in the causation of restenosis, wherein the vessel walls thicken in response to the trauma induced by the expanding stent.
Hence, in light of the above, those skilled in the art have recognized a need for a stent to implant in a body vessel that will reduce the likelihood of thrombosis, restenosis, and blood clotting. The present invention satisfies these needs as well as others.
The present invention addresses the above mentioned needs by providing a stent that induces a rotational motion in blood flowing therethrough, thus lessening the likelihood of thrombus and blood clot formation.
Briefly and in general terms, in one aspect the present invention is directed to a stent with an inner layer that is formed with a channel along its inner surface. The channel extends generally between the ends of the stent and directs a portion of the blood flowing therethrough in a generally circular direction with respect to the normal direction of blood flow.
In another aspect, the layer is formed with multiple channels to direct blood flow. The channel or channels may extend around the longitudinal axis of the stent forming a plurality of turns, thus describing a helix, to less than a full, 360 degree turn to impart only a slight rotational motion to the blood flow.
More specifically, the layer includes a polymeric material that has a channel cut by a laser or a blade or equivalent thereof while the polymeric material is in the form of a sheet, following which the sheet is rolled up to form a structure suitable to attaching to the interior of a stent. Alternatively, the channel may be formed by a strip disposed on the polymeric sheet to define the channel. In a still further embodiment, the inner layer may be cast as a unitary, generally tubular piece with the channel impressed into the layer by the casting mold.